A case of Legionella pneumophila evaluated with CT and ultrasound

Legionella pneumophila: The Journey from the Environment to the Blood

An outbreak of a potentially fatal form of pneumonia in 1976 and in the annual convention of the American Legion was the first time that Legionella spp. was identified. Thereafter, the term Legionnaires’ disease (LD) was established. The infection in humans is transmitted by the inhalation of aerosols that contain the microorganisms that belong to the Legionellaceae family and the genus Legionella. The genus Legionella contains genetically heterogeneous species and serogroups. The Legionella pneumophila serogroup 1 (Lp1) is the most often detected strain in outbreaks of LD. The pathogenesis of LD infection initiates with the attachment of the bacterial cells to the host cells, and subsequent intracellular replication. Following invasion, Legionella spp. activates its virulence mechanisms: generation of specific compartments of Legionella-containing vacuole (LCV), and expression of genes that encode a type IV secretion system (T4SS) for the translocation of proteins. The ability of L. pneumophila to transmigrate across the lung’s epithelium barrier leads to bacteremia, spread, and invasion of many organs with subsequent manifestations, complications, and septic shock. The clinical manifestations of LD depend on the bacterial load in the aerosol, the virulence factors, and the immune status of the patient. The infection has two distinct forms: the non- pneumatic form or Pontiac fever, which is a milder febrile flu-like illness, and LD, a more severe form, which includes pneumonia. In addition, the extrapulmonary involvement of LD can include heart, brain, abdomen, and joints.

Legionella Pneumonia on Point-of-care Ultrasound in the Emergency Department: A Case Report

Introduction

Legionella is an uncommon, atypical organism that can cause community-acquired pneumonia. Commonly associated with high fevers, gastrointestinal symptoms, and hyponatremia, it can be easily overlooked, especially during the coronavirus disease of 2019 (COVID-19) pandemic. Legionella has specific antibiotic treatment that will improve outcome; thus, its recognition is important.

Case Report

We present a case of Legionella pneumonia in a man presenting with shortness of breath and fever. The patient’s initial chest radiography was negative. With the use of point-of-care ultrasound (POCUS) the changes of atypical pneumonia could be seen. Ultimately Legionella was confirmed with urine antigen testing, and appropriate antibiotic treatment was started.

Discussion

Given the increased awareness of COVID-19 it is important to consider a broad differential with respiratory illness. Legionella pneumonia on POCUS is consistent with atypical pneumonia descriptions on ultrasound. Point-of-care ultrasound can be used to diagnose atypical pneumonia, specifically caused by Legionella in our case.

Conclusion

Legionella is evident on POCUS but is difficult to distinguish from other infections with POCUS alone. One should consider Legionella if POCUS is positive for signs of atypical infection.